In the next generation wireless communications system, a relay station (RS) is being introduced so as to increase cell coverage and to enhance a data transmission rate.
In the conventional wireless communications system using a relay station, there are not only wireless resources which consist of time or a frequency between a base station (BS) and a mobile station (MS), but also wireless resources between BS-RS, and wireless resources between RS-MS. Since a signal between BS-RS may be different from a signal between RS-MS, interference may occur when using the same wireless resources. This may lower the performance. In order to prevent this, has been considered a cooperative silencing technique in which the base station transmits no signal when the relay station transmits data.
However, the cooperative silencing technique may have the following problems. Firstly, since the BS is in an idle state using no wireless resources at a transmission section between the RS and the MS, a resource loss may occur. In order to solve this, the BS may also transmit a signal to the MS in a link between the BS and the MS by using the same wireless resources as wireless resources used for a transmission between the RS and the MS. This may enhance a receiving performance through a diversity effect. For instance, an antenna between the BS and the RS may be used to implement one space time coding.
In order to apply the above technique, required is scheduling information corresponding to data to be transmitted by the RS. In a cooperative transmission scheme between the BS and the RS, cooperative transmission data transmitted to the RS from the BS has to be successfully delivered.
However, in a substantial communication environment, the RS may not successfully receive cooperative transmission data transmitted from the BS. [7] In spite of this problem, the conventional art has proposed no method for preventing a transmission error in a link between the BS and the RS.
Since there is no consideration about a transmission error in a link between the BS and the RS in the conventional art, when the RS has not successfully received data transmitted from the BS, wireless resources pre-allocated so as to be transmitted to the MS may be wasted. Furthermore, since the BS and the RS do not perform an effective cooperative transmission, transmission efficiency to the MS may be lowered and long time delay may occur.